Recombinant protein expression in insect cell systems

Since the introduction of baculovirus expression vectors, the suitability of insect cells for the expression of functionally active genes of eukaryotic origin has been exhaustively documented. Originally realization of a functional viral expression vector was laborious and depended on double homologous in vivo recombination success as well as successful purification of recombinant baculovirus by plaque assay. Using the commercial Bac to Bac(TM) expression system we confirm that transposon-assisted recombination and cloning of recombinant transfectable bacmid DNA in bacteria now allow fast productive expression of a gene of interest. As an alternative to the expression by infected cells which sometimes suffers from the effects induced by cell lysis, we developed a stable Drosophila S-2 cell transformation protocol using the constitutive promoter of the immediate early gene of the silkworm baculovirus (BmNPV). Although baculovirus immediate early gene promoters are reported to be rather weak promoters, we routinely obtain expression levels up to the same range as obtained with the baculovirus system.